The role of adatoms for F4TCNQ adsorption on Au(111)

Organic adlayers on inorganic surfaces often contain adatoms, which can be incorporated within the adlayer and form well‑ordered frameworks. This causes notable modification of interface properties such as the adsorption geometries or the electronic structure of the adsorbed molecules.

Here we use DFT to study prototypical monolayers of F4TCNQ on Au(111), a system that is well‑known for embedding adatoms. In detail we investigate adatom‑caused modifications in the adsorption geometry, adsorption energy, charge transfer, and general electronic structure.

To study the adsorption geometry within the experimentally confirmed unit cell, geometry optimizations were performed for the adlayer with and without adatoms, yielding different adsorption geometries due to alteration of the electronic structure.

An analysis of the electronic states reveals an adatom‑driven modification of the occupation of adlayer states. This causes a substantial change in the net charge transfer at the interface, and, therefore, the work function at the interface. Furthermore, adatoms introduce interactions between neighboring adsorbate molecules via covalent coupling to the molecules. This covalent bonding character within the adlayer causes significant dispersion for adlayer bands at the Fermi level.